Process for refining bismuth



Patented .lu'l azs, 1931" UNITED STATES WALTER C. SIM. OI MOYLAN, PENNSYLVANIA, AND PETER MACK, JR., OF LA PUNDICION, PERU, ASSIGNORS, BY DIRECT AND MESNE ASSIGNMENTS, 013 ON E-HALF TO THE CERRO DE PASCO COPPER CORPORATION, OF NEW YORK, N. Y., A CORPORA- TION OI NEW YORK, AND ONE-HALF TO ANACONDA COPPER MINING COMPANY, OF ANACONDA, MONTANA, A CORPORATION OF MONTANA PROCESS FOR REFINING BISMUTH Drawing.-

until no more than a trace of lead and zinc remain in the alloy. In, ractisewe prefer to purify bismuth al loys y passin chlorine gas through the molten mass. ehave discovered that leadchloride and zinc chloride are formed and eliminated before the bismuth is seriouslyat tacked by the chlorine.

metal and hence rise to the surface of the molten mass. If themass is at a low temzaperature, these chlorides form a slag" or 'molten layer on top of the bismuth metal and very ttle is lost in the form of vapors. If hi her temperatures are used some of the chlorides are volatilized from the bismuth and slag. The fumes may be recovered in any convenient manner, for example, by water scrubbing or by the Gottrell precipitation.

under a blag blanket especiall added, so that .the volatilization and loss 0 zinc and lead I may be retarded from the start, and in order that the layer of sla may be of suificient depth to prevent vo atilization. For ex-' am e wemay cover over the molten alloy wi slag' obtained from previous chlorina- The chlorides of zinc and lead are lighter than the bismuth In practise we prefer to conduct the ch10 Application filed February 6, 1929. Serial No. 337,8805.

tion operations or with a mixture of molten salts such as the chlorides of sodium, potassium, lead, and/or zinc. The effect of chlorination will of course be to increase the quantity of the coveringsince this covering will-ab sbrb the zinc and lead chlorides formed.

The thermodynamical featuresof the-prod ess are indicated by the heats of formation of the chlorides as shown in the tabulation hereafter appended. 4

H eats of formation Per mole- Per chlo- I cule tine atom Zinc amends 91 400 4a 700 Lead chloride 841 -4- 421220 Bismuth chloride 90, 800 30, 233

Transition points Melting Boiling point point Zinc chloride... 365 0 732;? 0 Lead chloride- 498 C 954. 4 0 Bismuth chloride" 227 C 442. 2 C

From the data presented it is'apparent that the practicality of'the process is in a large measure dependent on the relative heats of formation of the'chlorides, for bismuth chloride is by far the most volatile of the three substances and, if formed, would be rapidly volatilized at a relatively low temperature. .4 i

Our experiments have indicated that an appreciable loss of bismuth does-occur when the molten alloy is chlorinated at temperatures of 500600 C.i.e. above the boiling point of bismuth chloride. However, the process has been found to be practicable, even at these elevated temperatures, as is illustrated by the foll'owingexample:

Ewample I An alloy containing 190% bismuth, 10%

of lead, and 1% of zinc was melted and maintained at a temperature of 500-600 C. Chlorine gas was passed into the alloy. Fumes of metallic chlorides and excess ch10.- rine arose from the mass and a thin layer of white slag (metallic chlorides) collected on names to this specification on the dates and the surface of the molten metal. The chloat the places hereinafter indicated rination was continued until the metal con- On Mar. 9th, 1929, at New York, N. Y.

tained only traces of lead and zinc. In con- WALTER C. SMITH. 5 ducting the purification to this degree, 9% On April 9, 1929, at La .Oroya, Peru. 70

of the bismuth was removed, though this PETER MACK, JR. was found to be recoverable from the mixture of metallic chlorides.

10 Example I I n An alloy containing 75% bismuth and 25% lead was melted and maintained at a temperature of about 400 C. Chlorine was passed in, and a thick layer of lead chloride soon formed on the surface of the molten mass. 80

The chlorination was continued until only a trace of lead remained in the molten metal, the loss of bismuth (to the slag) amounting to about 3%. Subsequent to the chlorination operation, the mixture was allowed to cool i 35 and the lead chloride was removed from the surface of the bismuth.

It may be remarked that certain metallic impurities, such as silver, antimony, and arsenic, cannot conveniently be removed by our on process because the chlorides of these substances have heats of formation even lower than that of bismuth chloride. These substances may be removed by other known methods. For example, the silver may be removed by the well-known zincing process in which zinc is added to the molten alloy and the crusts of impurities formed are removed by skimming. The arsenic and antimony 35 may be removed by treating the molten metal wgh caustic soda, and by other known meth- The presence of small quantities of impurities of the type mentioned does not inter- 40 fere with the operation of our process-in fact such impurities are nearly always present in the material undergoing treatment.

Chlorine is by far the cheapest of the halo- (glans and for this reason we have specifically chlorine gas. It should be understood, how-- ever, that from a chemical point of view the other halogens, notably bromine, may be used to replace chlorine.

We claim:

1. A process for removing lead and/or .zinc from a bismuth alloy which comprises heating said alloy to about 400 C. passing chlorine gas into said molten alloy, and separat- 12o ing the resultant metallic chlorides from the purified bismuth. f 2. A process for removing lead and/or zinc from a; bismuth alloy which comprises heating said alloy to about 400 C. under slag from previous chlorinations, passing chlorine gas into said molten alloy, and separating the resultant metallic chlorides from the purified bismuth.

' r 5 In testimony whereof, we have signed our escribed our process as it is applied with 110 

